1. Field of the Invention
The present invention relates to a ceramic stack which includes a plurality of ceramic plates having different lengths, a method of producing the ceramic stack, a piezoelectric/electrostrictive device which uses the ceramic stack as a substrate, a method of producing the piezoelectric/electrostrictive device, and a ceramic sintered body.
2. Description of the Related Art
In general, a ceramic stack is manufactured by stacking a plurality of ceramic plates having an identical length, or for example, a ceramic stack 204 is manufactured by stacking a plurality of ceramic plates 200, 202 having different lengths as shown in FIGS. 17 and 18.
The former ceramic stack involves no problem as to strength. However, the latter ceramic stack 204 involves some problem as to strength especially when the long ceramic plate 200 is used as a resonance member, because stress concentration is caused at a border 210 between a first principal surface 206 of the long ceramic plate 200 and a side surface 208 of the short ceramic plate 202 stacked on the first principal surface 206.
Accordingly, for example, a paste 212 is applied to the border 210 so that a bulged reinforcing member 214 having a circular arc-shaped cross section is added to the border 210 as shown in FIG. 17. Alternatively, as shown in FIG. 18, a concaved reinforcing member 216 having a circular arc-shaped cross section is added to the border 210.
However, a conventional example shown in FIG. 17 is equivalent to the case where the length of the short ceramic plate 202 is increased by a length of the reinforcing member 214. That is, when the long ceramic plate 200 is used as a resonance member, the stress is concentrated on a contact portion 218 between the first principal surface 206 of the long ceramic plate 200 and the circular arc-shaped surface of the reinforcing member 214. There is still a problem as to the strength.
Further, when the reinforcing member 214 having a certain thickness is attached to the long ceramic plate 200 to serve as the resonance member, the displacement amount of the long ceramic plate 200 is decreased in an amount corresponding thereto, and the resonance frequency is increased.
On the other hand, in order to add the concave one having the circular arc-shaped cross section to the border 210 as in a conventional example shown in FIG. 18, surface tension of liquid is utilized. In such a case, it is necessary to suppress the viscosity of the paste 212 to be extremely low by increasing the amount of water contained in the paste 212 for the reinforcing member 216. However, when the ceramic stack 204 is manufactured, the sintering step is performed after the application of the paste 212. Therefore, all of water in the paste 212 is evaporated in the sintering step. It is difficult to add the concaved reinforcing member 216 having the circular arc-shaped cross section to the border 210. Further, when the thickness of the short ceramic plate 202 is not more than 50 μm, it is impossible to add any concaved one having a circular arc-shaped cross section to the border 210.